BACKGROUND: Left atrial (LA) enlargement has been acknowledged as a significant predictor of cardiovascular morbidity and mortality. METHODS: To evaluate the accuracy of two-dimensional and three-dimensional echocardiography for determining LA volume, LA volume measurements by echocardiography were compared with those measured by 64-slice multidetector computed tomography (MDCT) as a reference standard. RESULTS: Fifty-seven consecutive patients (mean age, 66 ± 11 years; 59% men) referred to echocardiography and MDCT on the same day were prospectively evaluated. LA volume by three-dimensional echocardiography was correlated closely with that by MDCT (r = 0.95, P < .0001), with 8% underestimation. LA volume by two-dimensional echocardiography was correlated less well with that measured by MDCT (r = 0.86, P < .0001) and consistently underestimated LA volume by 19%, particularly as the left atrium enlarged. CONCLUSIONS: LA volume assessment by three-dimensional echocardiography was correlated closely with that measured by MDCT, albeit with an 8% underestimation. Three-dimensional echocardiography is a feasible noninvasive method to evaluate LA volume.